Imaging lens

ABSTRACT

An imaging lens includes a first lens having positive refractive power; a second lens having negative refractive power; a third lens; a fourth lens having negative refractive power; a fifth lens having positive refractive power; and a sixth lens, arranged in this order from an object side to an image plane side. The first lens is formed so that a surface thereof on the object side has a positive curvature radius. The second lens is formed so that a surface thereof on the image plane side has a positive curvature radius. The fifth lens is formed so that a surface thereof on the object side and a surface thereof on the image plane side have negative curvature radii. Each of the third lens, the fourth lens, the fifth lens, and the sixth lens has refractive power weaker than that of each of the first lens and the second lens.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to an imaging lens for forming an image ofan object on an imaging element such as a CCD sensor and a CMOS sensor.In particular, the present invention relates to an imaging lens suitablefor mounting in a relatively small camera such as a camera mounted in aportable device including a cellular phone and a portable informationterminal, a digital still camera, a security camera, a vehicle onboardcamera, and a network camera.

In these years, in place of cellular phones that are intended mainly formaking phone calls, so-called “smartphones” have been more widely used,i.e., cellular phones with such functions as those of portableinformation terminals (PDA) and/or personal computers. Since thesmartphones generally have more functions than those of the cellularphones, it is possible to use images taken by a camera thereof invarious applications. For example, while it is possible to use thesmartphones for printing and enjoying images taken, it is also possibleto use images in other usage such as processing images to use for gamecharacters or for makeup simulations, dress fitting simulations, and theothers. The ways of the image usage were not conventionally common,however, it becomes more common mainly among young people.

Generally speaking, a product group of cellular phones and smartphonesis often composed of products with various specifications including fromthe ones for beginners to the ones for advanced users. Among them, animaging lens to be mounted in the cellular phone or the smartphone,which is developed for advanced users, is required to have a highresolution lens configuration so as to be also applicable to a highpixel count imaging element of these days. However, as the imaging lensto be mounted in smartphones used for the above-described usages, it iscritical to have a small size with a wide angle of view, that is, a wideangle, rather than having a high resolution. Especially in these days,with downsizing and high functionality of smartphones, there are demandsfor an imaging lens having even smaller size and wider angle.

However, it is also true that even products for beginners are requiredto have some high resolution. In case of a lens configuration composedof six lenses, since the number of lenses that compose an imaging lensis many, although it is somewhat disadvantageous for downsizing of theimaging lens, since there is high flexibility upon designing, it haspotential of attaining satisfactory aberration correction and downsizingin a balanced manner. For example, as a lens configuration composed ofsix lenses, an imaging lens described in Patent Reference is known.

The imaging lens described in Patent Reference includes a first lensthat is negative and has a shape of a meniscus lens directing a convexsurface thereof to an object side; a bonded lens composed of two lenses,positive and negative lenses; and a positive fourth lens; a bonded lenscomposed of two lenses, positive and negative lenses, arranged.According to the imaging lens of Patent Reference, satisfyingconditional expression related to curvature radii of an object-sidesurface and an image plane-side surface of the first lens and aconditional expression related to the two bonded lenses, respectively,it is achievable to satisfactorily correct a distortion and a chromaticaberration.

-   Patent Reference Japanese Patent Application Publication No.    2011-145315

However, in case of the imaging lens of Patent Reference, since adistance from an object-side surface of the first lens to an image planeof an imaging element is long, it is necessary to bend an optical pathby arranging a prism or a mirror between an imaging lens and an imageplane, in order to mount the imaging lens in a small-sized camera suchas a cellular phone or a smartphone. High functionality and downsizingof cellular phones and smartphones have been advanced every year, andthe level of downsizing required for an imaging lens is even higher thanbefore. With the lens configuration described in Patent Reference, it isdifficult to attain satisfactory aberration correction while attainingdownsizing of the imaging lens so as to meet the demands.

Here, such challenge is not a problem specific to the imaging lens to bemounted in cellular phones and smartphones, and rather, it is a commonproblem even for an imaging lens to be mounted in a relatively smallcamera such as digital still cameras, portable information terminals,security cameras, vehicle onboard cameras, and network cameras.

In view of the above-described problems in the conventional techniques,an object of the invention is to provide an imaging lens that cansatisfactorily correct aberrations. A further object of the invention isto provide an imaging lens that can attain both downsizing of theimaging lens and satisfactory aberration correction.

Further objects and advantages of the invention will be apparent fromthe following description of the invention.

SUMMARY OF THE INVENTION

In order to attain the objects described above, according to a firstaspect of the invention, an imaging lens includes a first lens havingpositive refractive power; a second lens having negative refractivepower; a third lens; a fourth lens having negative refractive power; afifth lens having positive refractive power; and a sixth lens, arrangedin this order from an object side to an image plane side. The first lenshas an object-side surface having a positive curvature radius. Thesecond lens has an image plane-side surface having a positive curvatureradius. The fifth lens has an object-side surface and an imageplane-side surface, both of which have negative curvature radii. Inaddition, each lens from the third lens through the sixth lens hasweaker refractive power than that of each of the first lens and thesecond lens.

According to the first aspect of the present invention, in the imaginglens having the above-described configuration, the first lens and thesecond lens have stronger refractive power than that of each of otherlenses. Accordingly, aberrations are roughly corrected with those twolenses, and aberrations not corrected with the first lens and the secondlens are more finely corrected with the third to the sixth lenses thathave weaker refractive power than the first and the second lenses.Therefore, it is possible to mainly correct axial aberrations in thefirst lens and the second lens, and to mainly correct off-axisaberrations in the third to the sixth lenses, so that it is possible tosatisfactorily correct aberrations in a balanced manner in the wholelens system. Moreover, since the first lens and the second lens, whichare arranged on the object side in the imaging lens, have relativelystrong refractive power, it is possible to contribute to satisfactorycorrection of aberrations and also to downsizing of the imaging lens.

According to a second aspect of the present invention, in the imaginglens having the above-described configuration, the fourth lens may bepreferably formed in a shape such that curvature radii of an objectside-surface and the image plane-side surface are both negative. Asdescribed above, the fifth lens is formed in a shape such that curvatureradii of the object-side surface and the image plane-side surface areboth negative. Forming the fourth lens in a similar shape to that of thefifth lens, i.e., a shape of a meniscus lens directing a concave surfacethereof to the object side near an optical axis, it is possible tofurther satisfactorily correct aberrations.

According to a third aspect of the present invention, in the imaginglens having the above-described configuration, the sixth lens may bepreferably formed in a shape such that curvature radii of theobject-side surface and the image plane-side surface are both positive.

According to the imaging lens having the above-described configuration,the fifth lens and the sixth lens are preferably formed as asphericshapes such that an object-side surface thereof and an imageplane-surface thereof have an inflexion point. According to the imaginglens of the invention, the third to the sixth lenses serve forsatisfactorily correcting off-axis aberrations as well as axialaberrations. The fifth lens and the sixth lens, which are close to theimage plane, especially play a significant role in correcting off-axisaberrations. Forming each of the fifth lens and the sixth lens asaspheric shapes having an inflexion point, it is possible tosatisfactorily correct off-axis aberrations, and also to easily restrainan incident angle of a light beam emitted from the imaging lens to theimage plane within a range set in advance. An imaging lens of a CCDsensor, a CMOS sensor or the like, a range of incident angle of a lightbeam that can be taken in a sensor (so-called “chief ray angle”) is setin advance. By restraining the incident angle of a light beam emittedfrom an imaging lens to an image plane within the range set in advance,it is possible to restrain generation of shading, i.e., a phenomenonthat causes a dark periphery of an image.

According to a fourth aspect of the present invention, when the firstlens has a focal length f1 and the second lens has a focal length f2,the imaging lens having the above-described configuration preferablysatisfies the following conditional expression (1):−0.7<f1/f2<−0.3  (1)

When the imaging lens satisfies the conditional expression (1), it ispossible to suitably attain downsizing of the imaging lens whilesatisfactorily correcting chromatic aberration and astigmatism. When thevalue exceeds the upper limit of “−0.3”, since the negative refractivepower of the second lens is relatively weaker than the positiverefractive power of the first lens, although it is advantageous fordownsizing of the imaging lens, it is difficult to secure a back focallength. In addition, since an axial chromatic aberration isinsufficiently corrected (a focal position at a short wavelength movestowards the object side relative to a focal position at a referencewavelength) and an astigmatic difference increases, it is difficult toobtain satisfactory image-forming performance. On the other hand, whenthe value is below the lower limit of “−0.7”, since the refractive powerof the second lens is relatively stronger than that of the first lens,although it is easy to secure back focal length, it is difficult toattain downsizing of the imaging lens.

Moreover, the axial chromatic aberration is excessively corrected (afocal position at a short wavelength moves towards the image plane siderelative to a focal position at a reference wavelength) and an off-axischromatic aberration of magnification is excessively corrected (animage-forming point at a short wavelength moves in a direction to beaway from an optical axis relative to an image-forming point at areference wavelength). In addition, since astigmatism increases, also inthis case, it is difficult to obtain satisfactory image-formingperformance.

According to a fifth aspect of the present invention, when a whole lenssystem has a focal length f, and a composite focal length of the firstlens and the second lens is f12, the imaging lens having theabove-described configuration preferably satisfies the followingconditional expression (2):0.8<f12/f<1.5  (2)

When the imaging lens satisfies the conditional expression (2), it ispossible to restrain the axial chromatic aberration, a coma aberration,and the astigmatism within a satisfactory range, while attainingdownsizing of the imaging lens. When the value exceeds the upper limitof “1.5”, the negative refractive power of the second lens is strongrelative to the positive refractive power of the first lens, andalthough it is easy to correct an axial chromatic aberration, but it isdifficult to attain downsizing of the imaging lens. In addition, sincethe astigmatic difference increases, it is difficult to obtainsatisfactory image-forming performance. When the value is below thelower limit of “0.8”, since the positive refractive power of the firstlens is relatively strong, although it is advantageous for downsizing ofthe imaging lens, the back focal length is short, so that it isdifficult to secure space for disposing an insert such as an infraredcut-off filter. Furthermore, the axial chromatic aberration isinsufficiently corrected and the coma aberration increases, so that itis difficult to obtain satisfactory image-forming performance.

According to a sixth aspect of the present invention, when a whole lenssystem has a focal length f and the fourth lens has a focal length f4,the imaging lens having the above-described configuration preferablysatisfies the following conditional expression (3):−0.3<f/f4<−0.01  (3)

When the imaging lens satisfies the conditional expression (3), it ispossible to restrain a distortion and a field curvature withinsatisfactory ranges while attaining downsizing of the imaging lens. Inaddition, it is also possible to restrain the incident angle of a lightbeam emitted from the imaging lens to an imaging element within a rangeset in advance. According to the imaging lens of the invention, thefourth lens has negative refractive power. Restraining the negativerefractive power of the fourth lens within the range of the conditionalexpression, it is possible to restrain aberrations within satisfactoryranges. When the value exceeds the upper limit of “−0.01”, although itis advantageous for downsizing of the imaging lens, it is difficult tosecure the back focal length. In addition, a minus distortion increasesat a periphery of an image plane and a periphery of the image surfacecurves to the minus direction, so that it is difficult to obtainsatisfactory image-forming performance. On the other hand, when thevalue is below the lower limit of “−0.3”, since a distance from an imageplane to an exit pupil is long, although it is easy to restrain theincident angle of a light beam emitted from the imaging lens to theimaging element within the range set in advance, the image surfacecurves in a plus direction and the plus distortion increases, so that itis difficult to obtain image-forming performance also in this case.

According to a seventh aspect of the present invention, when a wholelens system has a focal length f and a composite focal length of thethird lens and the fourth lens is f34, the imaging lens having theabove-described configuration preferably satisfies the followingconditional expression (4):−20.0<f34/f<−1.0  (4)

When the imaging lens satisfies the conditional expression (4), it ispossible to restrain the chromatic aberration, the field curvature, andthe astigmatism within satisfactory ranges. In addition, it is alsopossible to restrain the incident angle of a light beam emitted from theimaging lens to the imaging element within a range set in advance. Whenthe value exceeds the upper limit of “−1.0”, since a distance from animage plane to an exit pupil is long, it is easy to restrain theincident angle of a light beam emitted from the imaging lens to theimaging element within a range set in advance. However, the axialchromatic aberration and the chromatic aberration of magnification areexcessively corrected and a plus distortion increases, it is difficultto obtain satisfactory image-forming performance. On the other hand,when the value is below the lower limit of “−20.0”, the axial chromaticaberration is insufficiently corrected. In addition, a sagittal imagesurface curves to the object side (in a minus direction) and theastigmatic difference increases, so that it is difficult to obtainsatisfactory image-forming performance.

According to an eighth aspect of the present invention, when a distanceon the optical axis from the image plane-side surface of the second lensto the object-side surface of the third lens is D23 and a distance onthe optical axis from the object-side surface of the first lens to theimage plane-side surface of the sixth lens is L16, the imaging lenshaving the above-described configuration preferably satisfies thefollowing conditional expression (5):0.05<D23/L16<0.3  (5)

When the imaging lens satisfies the conditional expression (5), it ispossible to restrain a spherical aberration within a satisfactory rangewhile attaining downsizing of the imaging lens. In addition, it is alsopossible to restrain the incident angle of a light beam emitted from theimaging lens to the imaging element within a range set in advance. Whenthe value exceeds the upper limit of “0.3”, although it is easy torestrain the spherical aberration within a satisfactory range andrestrain the incident angle of a light beam emitted from the imaginglens to the imaging element within the range set in advance, it isdifficult to secure the back focal length. On the other hand, when thevalue is below the lower limit of “0.05”, although it is advantageousfor downsizing of the imaging lens, a spherical aberration increases andit is difficult to obtain satisfactory image-forming performance. Inaddition, it is difficult to restrain the incident angle of a light beamemitted from the imaging lens to the imaging element within the rangeset in advance.

According to a ninth aspect of the present invention, when the firstlens has an Abbe's number νd1, the fourth lens has an Abbe's number νd4,the fifth lens has an Abbe's number νd5, and the sixth lens has anAbbe's number νd6, the imaging lens having the above-describedconfiguration preferably satisfies the following conditional expressions(6) through (9):45<νd1<75  (6)45<νd4<75  (7)45<νd5<75  (8)45<νd6<75  (9)

When the imaging lens satisfies the conditional expressions (6) through(9), it is possible to satisfactorily correct the axial and the off-axischromatic aberrations. Having the Abbe's numbers of four lenses in thesix lenses larger than the lower limit of “45”, it is possible toeffectively restrain the chromatic aberration generated in those fourlenses, so that it is possible to suitably restrain the chromaticaberration of the whole lens system within satisfactory range. Moreover,having the Abbe's number of each lens smaller than the upper limit of“75”, it is possible to restrain cost of lens materials.

According to a tenth aspect of the present invention, in order to moresatisfactorily correct the axial and the off-axis chromatic aberrations,when the second lens has an Abbe's number νd2 and the third lens has anAbbe's number νd3, the imaging lens having the above-describedconfiguration preferably satisfies the conditional expressions (10) and(11):20<νd2<40  (10)20<νd3<40  (11)

According to the imaging lens of the invention, it is possible toprovide an imaging lens with satisfactorily corrected aberrations. Inaddition, it is possible to provide a small-sized imaging lensespecially suitable for mounting in a small-sized camera, while havinghigh resolution with satisfactorily corrected aberrations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 1 according to an embodiment of theinvention;

FIG. 2 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 1;

FIG. 3 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 1;

FIG. 4 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 2 according to the embodiment of theinvention;

FIG. 5 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 4;

FIG. 6 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 4;

FIG. 7 shows a sectional view of a schematic configuration of an imaginglens in Numerical Data Example 3 according to the embodiment of theinvention;

FIG. 8 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 7;

FIG. 9 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 7;

FIG. 10 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 4 according to the embodiment ofthe invention;

FIG. 11 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 10;

FIG. 12 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 10;

FIG. 13 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 5 according to the embodiment ofthe invention;

FIG. 14 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 13;

FIG. 15 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 13;

FIG. 16 shows a sectional view of a schematic configuration of animaging lens in Numerical Data Example 6 according to the embodiment ofthe invention;

FIG. 17 is an aberration diagram showing a lateral aberration of theimaging lens of FIG. 16; and

FIG. 18 is an aberration diagram showing a spherical aberration,astigmatism, and a distortion of the imaging lens of FIG. 16.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereunder, referring to the accompanying drawings, embodiments of thepresent invention will be fully described.

FIGS. 1, 4, 7, 10, 13, and 16 are schematic sectional views of imaginglenses in Numerical Data Examples 1 to 6 according to the embodiment,respectively. Since a basic lens configuration is the same among thoseNumerical Data Examples, the lens configuration of the embodiment willbe described with reference to the illustrative sectional view ofNumerical Data Example 1.

As shown in FIG. 1, the imaging lens of the embodiment includes a firstlens L1 having positive refractive power; a second lens L2 havingnegative refractive power; a third lens L3; a fourth lens L4 havingnegative refractive power; a fifth lens L5 having positive refractivepower; and a sixth lens L6, arranged in the order from an object side toan image plane side. The imaging lenses of Numerical Data Examples 1 to5 are examples in which the third lens L3 has negative refractive power,and the imaging lens of Numerical Data Example 6 is an example in whichthe third lens L3 has positive refractive power. The imaging lenses ofNumerical Data Examples 1 to 5 are also examples in which the sixth lensL6 has negative refractive power, and the imaging lens of Numerical DataExample 6 is an example in which the sixth lens L6 has positiverefractive power. Here, a filter 10 is disposed between the sixth lensL6 and an image plane IM. This filter 10 can be optionally omitted.

According to the imaging lens of the embodiment, refractive power ofeach lens from the third lens L3 to the sixth lens L6 is weaker thanthat of each refractive power of the first lens L1 and the second lensL2. In other words, when the first lens L1 has a focal length f1, thesecond lens L2 has a focal length f2, the third lens L3 has a focallength f3, the fourth lens L4 has a focal length f4, the fifth lens L5has a focal length f5, and the sixth lens has a focal length f6, theimaging lens of the embodiment satisfies the relation, (f1, |f2|)<(|f3|,|f4|, f5, |f6|).

According to the imaging lens having the above-described configuration,the first lens L1 is formed in a shape such that a curvature radius r1of an object-side surface thereof is positive and a curvature radius r2of an image plane-side surface thereof is negative, so as to be a shapeof a biconvex lens near an optical axis X. The shape of the first lensL1 is not limited to the one in Numerical Data Example 1. The shape ofthe first lens L1 can be any as long as the curvature radius r1 of theobject-side surface thereof is positive. The imaging lenses of NumericalData Examples 1, 3, 5, and 6 are examples in which the shape of thefirst lens L1 has a shape of a biconvex lens near the optical axis X,and the imaging lenses of Numerical Data Examples 2 and 4 are examplesin which the first lens L1 is formed in a shape such that the curvatureradius r1 of the object side surface thereof and the curvature radius r2of the image plane-side surface thereof are both positive, i.e. a shapeof a meniscus lens directing a convex surface thereof to the object sidenear the optical axis X. Here, in the embodiment, a stop ST is providedon the image plane-side surface of the first lens L1.

The second lens L2 is formed in a shape such that a curvature radius r3of an object-side surface thereof and a curvature radius r4 of an imageplane-side surface thereof are both positive, so as to be a shape of ameniscus lens directing a convex surface thereof to the object side nearthe optical axis X. The shape of the second lens L2 can be any as longas the curvature radius r4 of the image plane-side surface is positive,and can be the one in which the curvature radius r3 of the objectside-surface thereof is negative, i.e. a biconcave lens near the opticalaxis X.

The third lens L3 is formed in a shape such that a curvature radius r5of an object-side surface thereof and a curvature radius r6 of an imageplane-side surface thereof are both negative, so as to be a shape of ameniscus lens directing a concave surface thereof to the object sidenear the optical axis X. The shape of the third lens L3 is not limitedto the one in Numerical Data Example 1. The imaging lenses of NumericalData Examples 1 and 3 to 6 are examples in which the shape of the thirdlens L3 is a shape of a meniscus lens directing a concave surfacethereof to the object side near the optical axis X, and the imaging lensof Numerical Data Example 2 is an example in which the shape of thethird lens L3 is a shape of a meniscus lens directing a convex surfacethereof to the object side near the optical axis X.

The fourth lens L4 is formed in a shape such that a curvature radius r7of an object-side surface thereof and a curvature radius r8 of an imageplane-side surface thereof are both negative, so as to be a shape of ameniscus lens directing a concave surface thereof to the object sidenear the optical axis X. In addition, the shape of the fourth lens L4can be a shape of a meniscus lens directing a concave surface thereof tothe object side near the optical axis X, or a shape of a biconcave lensnear the optical axis X. The fourth lens L4 can be formed in variousshapes as long as the refractive power thereof is negative.

The fifth lens L5 is formed in a shape such that a curvature radius r9of an object-side surface thereof and a curvature radius r10 of an imageplane-side surface thereof are both negative, so as to be a shape of ameniscus lens directing a concave surface thereof to the object sidenear the optical axis X. The sixth lens L6 is formed in a shape suchthat a curvature radius r11 of an object-side surface thereof and acurvature radius r12 of an image plane-side surface thereof are bothpositive, so as to be a shape of a meniscus lens directing a convexsurface thereof to the object side near the optical axis X.

According to the imaging lens of the embodiment, the fifth lens L5 andthe sixth lens L6 are formed as aspheric shapes such that an object-sidesurface thereof and an image plane-side surface thereof have aninflexion point. With such shapes, it is possible to satisfactorilycorrect off-axis aberrations. In addition, with the above-describedshapes of the fifth lens L5 and the sixth lens L6, it is possible toeasily secure telecentric characteristic, the incident angle of a lightbeam emitted from the imaging lens to the image plane IM is restrainedto an angle smaller than the chief ray angle that is set in advance foreach imaging element as a range of an incident angle of a light beamthat can be taken in a sensor.

The imaging lens of the embodiment satisfies the following conditionalexpressions (1) to (11):−0.7<f1/f2<−0.3  (1)0.8<f12/f<1.5  (2)−0.3<f/f4<−0.01  (3)−20.0<f34/f<−1.0  (4)0.05<D23/L16<0.3  (5)45<νd1<75  (6)45<νd4<75  (7)45<νd5<75  (8)45<νd6<75  (9)20<νd2<40  (10)20<νd3<40  (11)

In the above formulas,

f: Focal length of the whole lens system

f1: Focal length of the first lens L1

f2: Focal length of the second lens L2

f4: Focal length of the fourth lens L4

f12: Composite focal length of the first lens L1 and the second lens L2

f34: Composite focal length of the third lens L3 and the fourth lens L4

D23: Distance on the optical axis from the image plane-side surface ofthe second lens L2 to the object-side surface of the third lens L3

L16: Distance on the optical axis from the object-side surface of thefirst lens L1 to the image plane-side surface of the sixth lens L6

νd1: Abbe's number of the first lens L1

νd2: Abbe's number of the second lens L2

νd3: Abbe's number of the third lens L3

νd4: Abbe's number of the fourth lens L4

νd5: Abbe's number of the fifth lens L5

νd6: Abbe's number of the sixth lens L6

Here, it is not necessary to satisfy all of the conditional expressions,and it is achievable to obtain an effect corresponding to the respectiveconditional expression when any single one of the conditionalexpressions is individually satisfied.

In the embodiment, lens surfaces of each lens are formed as asphericsurfaces. When the aspheric surfaces applied to the lens surfaces havean axis Z in a direction of the optical axis X, a height H in adirection perpendicular to the optical axis X, a conical coefficient k,and aspheric coefficients A₄, A₆, A₈, A₁₀, A₁₂, A₁₄, and A₁₆, a shape ofthe aspheric surfaces of the lens surfaces is expressed as follows:

$\begin{matrix}{Z = {\frac{\frac{H^{2}}{R}}{1 + \sqrt{1 - {\left( {k + 1} \right)\frac{H^{2}}{R^{2}}}}} + {A_{4}H^{4}} + {A_{6}H^{6}} + {A_{8}H^{8}} + {A_{10}H^{10}} + {A_{12}H^{12}} + {A_{14}H^{14}} + {A_{16}H^{16}}}} & \lbrack{Formula}\rbrack\end{matrix}$

Next, Numerical Data Examples of the imaging lens of the embodiment willbe described. In each Numerical Data Example, f represents a focallength of the whole lens system, Fno represents an F number, and ωrepresents a half angle of view, respectively. In addition, i representsa surface number counted from the object side, r represents a curvatureradius, d represents a distance between lens surfaces (surface spacing)on the optical axis, nd represents a refractive index, and νd representsan Abbe's number, respectively. Here, surface numbers i affixed with *(asterisk) means the surfaces are aspheric.

Numerical Data Example 1

Basic data are shown below.

f = 4.20 mm, Fno = 2.1, ω = 35.2° Unit: mm Surface Data Surface Number ir d nd νd (Object) ∞ ∞  1* 1.471 0.741 1.5350 56.1 (=νd1)  2* (Stop)−41.542 0.023  3* 7.688 0.274 1.6355 24.0 (=νd2)  4* 2.282 0.569 (=D23) 5* −9.015 0.336 1.6355 24.0 (=νd3)  6* −10.214 0.056  7* −7.358 0.3691.5350 56.1 (=νd4)  8* −14.505 0.045  9* −6.877 0.407 1.5350 56.1 (=νd5)10* −5.636 0.088 11* 1.899 0.771 1.5350 56.1 (=νd6) 12* 1.509 0.200 13 ∞0.300 1.5168 64.2 14 ∞ 0.739 (Image ∞ plane) f1 = 2.66 mm f2 = −5.16 mmf3 = −134.38 mm f4 = −28.32 mm f5 = 52.18 mm f6 = −44.21 mm f12 = 4.25mm f34 = −23.14 mm L16 = 3.679 mm Aspheric Surface Data First Surface k= 0.000, A₄ = −5.471E−05, A₆ = 2.081E−03, A₈ = 1.807E−02, A₁₀ =−7.882E−02, A₁₂ = 9.308E−02, A₁₄ = −4.401E−02 Second Surface k = 0.000,A₄ = −4.050E−02, A₆ = 1.641E−01, A₈ = −2.787E−01, A₁₀ = 1.737E−01, A₁₂ =1.680E−02, A₁₄ = −5.626E−02 Third Surface k = 0.000, A₄ = −8.966E−02, A₆= 2.901E−01, A₈ = −5.618E−01, A₁₀ = 7.291E−01, A₁₂ = −5.072E−01, A₁₄ =1.446E−01 Fourth Surface k = 0.000, A₄ = −2.732E−02, A₆ = 1.022E−01, A₈= −1.233E−01, A₁₀ = 4.211E−01, A₁₂ = −5.788E−01, A₁₄ = 3.509E−01 FifthSurface k = 0.000, A₄ = −4.663E−02, A₆ = −3.118E−01, A₈ = 5.053E−01, A₁₀= −6.105E−01, A₁₂ = 5.949E−01, A₁₄ = −2.568E−01 Sixth Surface k = 0.000,A₄ = −4.837E−02, A₆ = −1.934E−01, A₈ = 2.493E−01, A₁₀ = −7.491E−02Seventh Surface k = 0.000, A₄ = −2.898E−01, A₆ = 5.505E−01, A₈ =−4.000E−01, A₁₀ = 1.407E−01, A₁₂ = −2.086E−02 Eighth Surface k = 0.000,A₄ = −3.946E−01, A₆ = 7.716E−01, A₈ = −8.063E−01, A₁₀ = 5.242E−01, A₁₂ =−2.067E−01, A₁₄ = 4.482E−02, A₁₆ = −4.122E−03 Ninth Surface k = 0.000,A₄ = 3.005E−01, A₆ = −3.073E−01, A₈ = 1.090E−01, A₁₀ = −1.396E−02, A₁₂ =2.132E−03, A₁₄ = −1.119E−03, A₁₆ = 1.661E−04 Tenth Surface k = 0.000, A₄= 3.418E−01, A₆ = −2.946E−01, A₈ = 1.103E−01, A₁₀ = −1.433E−02, A₁₂ =−4.780E−03, A₁₄ = 1.983E−03, A₁₆ = −1.984E−04 Eleventh Surface k =−7.791E−01, A₄ = −2.718E−01, A₆ = 1.638E−01, A₈ = −6.543E−02, A₁₀ =1.101E−02, A₁₂ = 2.571E−04, A₁₄ = −2.639E−04, A₁₆ = 1.996E−05 TwelfthSurface k = −6.551, A₄ = −8.910E−02, A₆ = 2.743E−02, A₈ = −4.841E−03,A₁₀ = −1.927E−03, A₁₂ = 1.152E−03, A₁₄ = −2.096E−04, A₁₆ = 1.322E−05 Thevalues of the respective conditional expressions (1) to (5) are asfollows: (1) f1/f2 = −0.52 (2) f12/f = 1.01 (3) f/f4 = −0.15 (4) f34/f =−5.51 (5) D23/L16 = 0.15

Accordingly, the imaging lens of Numerical Data Example 1 satisfies theabove-described conditional expressions. A distance on the optical axisX from the object-side surface of the first lens L1 to the image planeIM (length in air) is 4.82 mm, and downsizing of the imaging lens isattained.

FIG. 2 shows a lateral aberration that corresponds to a ratio H of eachimage height to the maximum image height (hereinafter referred to as“image height ratio H”), which is divided into a tangential directionand a sagittal direction (which is the same in FIGS. 5, 8, 11, 14, and17) in the imaging lens of Numerical Data Example 1. Furthermore, FIG. 3shows a spherical aberration (mm), astigmatism (mm), and a distortion(%), respectively, in the imaging lens of Numerical Data Example 1. Inthe aberration diagrams, for the lateral aberration diagrams andspherical aberration diagrams, aberrations at each wavelength, i.e. a gline (435.84 nm), an e line (546.07 nm), and a C line (656.27 nm) areindicated. In astigmatism diagram, an aberration on a sagittal imagesurface S and an aberration on a tangential image surface T arerespectively indicated (which are the same in FIGS. 6, 9, 12, 15, and18). As shown in FIGS. 2 and 3, according to the imaging lens ofNumerical Data Example 1, the aberrations are satisfactorily corrected.

Numerical Data Example 2

Basic data are shown below.

f = 4.61 mm, Fno = 2.0, ω = 32.7° Unit: mm Surface Data Surface Number ir d nd νd (Object) ∞ ∞  1* 1.713 0.761 1.5350 56.1 (=νd1)  2* (Stop)70.172 0.058  3* 7.625 0.309 1.6355 24.0 (=νd2)  4* 2.638 0.723 (=D23) 5* 8.695 0.317 1.6355 24.0 (=νd3)  6* 6.886 0.189  7* −14.611 0.4981.5350 56.1 (=νd4)  8* −20.256 0.052  9* −6.014 0.348 1.5350 56.1 (=νd5)10* −5.126 0.141 11* 1.836 0.901 1.5350 56.1 (=νd6) 12* 1.469 0.250 13 ∞0.300 1.5168 64.2 14 ∞ 0.653 (Image ∞ plane) f1 = 3.26 mm f2 = −6.44 mmf3 = −55.39 mm f4 = −100.76 mm f5 = 56.82 mm f6 = −95.74 mm f12 = 5.19mm f34 = −36.08 mm L16 = 4.297 mm Aspheric Surface Data First Surface k= 0.000, A₄ = 7.737E−03, A₆ = −2.527E−02, A₈ = 5.628E−02, A₁₀ =−6.839E−02, A₁₂ = 4.299E−02, A₁₄ = −1.158E−02 Second Surface k = 0.000,A₄ = −1.023E−01, A₆ = 2.115E−01, A₈ = −2.394E−01, A₁₀ = 1.602E−01, A₁₂ =−6.154E−02, A₁₄ = 9.655E−03 Third Surface k = 0.000, A₄ = −1.635E−01, A₆= 2.984E−01, A₈ = −3.331E−01, A₁₀ = 2.420E−01, A₁₂ = −1.058E−01, A₁₄ =2.218E−02 Fourth Surface k = 0.000, A₄ = −7.844E−02, A₆ = 1.435E−01, A₈= −1.608E−01, A₁₀ = 1.551E−01, A₁₂ = −9.688E−02, A₁₄ = 3.168E−02 FifthSurface k = 0.000, A₄ = −9.312E−02, A₆ = −1.363E−02, A₈ = 5.838E−02, A₁₀= −2.007E−01, A₁₂ = 1.697E−01, A₁₄ = −4.926E−02 Sixth Surface k = 0.000,A₄ = −1.823E−01, A₆ = 1.779E−01, A₈ = −1.456E−01, A₁₀ = 4.276E−02Seventh Surface k = 0.000, A₄ = −4.409E−01, A₆ = 5.705E−01, A₈ =−3.472E−01, A₁₀ = 1.071E−01, A₁₂ = −1.299E−02 Eighth Surface k = 0.000,A₄ = −4.680E−01, A₆ = 6.624E−01, A₈ = −6.818E−01, A₁₀ = 4.797E−01, A₁₂ =−2.026E−01, A₁₄ = 4.589E−02, A₁₆ = −4.276E−03 Ninth Surface k = 0.000,A₄ = 3.261E−01, A₆ = −2.920E−01, A₈ = 1.097E−01, A₁₀ = −1.424E−02, A₁₂ =−4.195E−03, A₁₄ = 1.887E−03, A₁₆ = −2.101E−04 Tenth Surface k = 0.000,A₄ = 3.433E−01, A₆ = −2.584E−01, A₈ = 8.531E−02, A₁₀ = −6.981E−03, A₁₂ =−4.528E−03, A₁₄ = 1.434E−03, A₁₆ = −1.260E−04 Eleventh Surface k =−8.377E−01, A₄ = −2.882E−01, A₆ = 1.513E−01, A₈ = −4.549E−02, A₁₀ =5.229E−03, A₁₂ = 1.543E−04, A₁₄ = −2.335E−05, A₁₆ = −4.869E−06 TwelfthSurface k = −6.143, A₄ = −6.398E−02, A₆ = 9.073E−03, A₈ = 4.646E−03, A₁₀= −3.459E−03, A₁₂ = 9.031E−04, A₁₄ = −1.084E−04, A₁₆ = 5.005E−06 Thevalues of the respective conditional expressions are as follows: f1/f2 =−0.51 f12/f = 1.13 f/f4 = −0.046 f34/f = −7.83 D23/L16 = 0.17

Accordingly, the imaging lens of Numerical Data Example 2 satisfies theabove-described conditional expressions. A distance on the optical axisX from the object-side surface of the first lens L1 to the image planeIM (length in air) is 5.40 mm, and downsizing of the imaging lens isattained.

FIG. 5 shows the lateral aberration that corresponds to the image heightratio H of the imaging lens in Numerical Data Example 2, and FIG. 6shows the spherical aberration (mm), the astigmatism (mm), and thedistortion (%), respectively. As shown in FIGS. 5 and 6, according tothe imaging lens of Numerical Data Example 2, the aberrations are alsosatisfactorily corrected.

Numerical Data Example 3

Basic data are shown below.

f = 4.87 mm, Fno = 2.3, ω = 31.3° Unit: mm Surface Data Surface Number ir d nd νd (Object) ∞ ∞  1* 1.538 0.715 1.5350 56.1 (=νd1)  2* (Stop)−38921.490 0.087  3* 16.514 0.500 1.6355 24.0 (=νd2)  4* 2.623 0.333(=D23)  5* −28.730 0.467 1.6355 24.0 (=νd3)  6* −30.158 0.095  7* −8.4720.426 1.5350 56.1 (=νd4)  8* −20.497 0.064  9* −5.263 0.448 1.5350 56.1(=νd5) 10* −4.946 0.136 11* 2.131 0.826 1.5350 56.1 (=νd6) 12* 1.6170.200 13 ∞ 0.300 1.5168 64.2 14 ∞ 0.877 (Image plane) ∞ f1 = 2.86 mm f2= −4.93 mm f3 = −1084.51 mm f4 = −27.23 mm f5 = 102.36 mm f6 = −28.41 mmf12 = 4.73 mm f34 = −26.40 mm L16 = 4.097 mm Aspheric Surface Data FirstSurface k = 0.000, A₄ = −1.799E−03, A₆ = 1.203E−03, A₈ = 2.196E−02, A₁₀= −7.820E−02, A₁₂ = 9.229E−02, A₁₄ = −4.398E−02 Second Surface k =0.000, A₄ = −5.353E−02, A₆ = 1.626E−01, A₈ = −2.759E−01, A₁₀ =1.744E−01, A₁₂ = 1.473E−02, A₁₄ = −5.807E−02 Third Surface k = 0.000, A₄= −8.293E−02, A₆ = 2.664E−01, A₈ = −5.712E−01, A₁₀ = 7.369E−01, A₁₂ =−5.001E−01, A₁₄ = 1.309E−01 Fourth Surface k = 0.000, A₄ = −3.985E−02,A₆ = 7.526E−02, A₈ = −1.382E−01, A₁₀ = 4.364E−01, A₁₂ = −5.632E−01, A₁₄= 3.057E−01 Fifth Surface k = 0.000, A₄ = −5.491E−02, A₆ = −3.272E−01,A₈ = 5.358E−01, A₁₀ = −6.029E−01, A₁₂ = 5.711E−01, A₁₄ = −2.637E−01Sixth Surface k = 0.000, A₄ = −3.175E−02, A₆ = −1.750E−01, A₈ =2.452E−01, A₁₀ = −8.143E−02 Seventh Surface k = 0.000, A₄ = −2.941E−01,A₆ = 5.535E−01, A₈ = −3.953E−01, A₁₀ = 1.407E−01, A₁₂ = −2.327E−02Eighth Surface k = 0.000, A₄ = −3.866E−01, A₆ = 7.724E−01, A₈ =−8.079E−01, A₁₀ = 5.238E−01, A₁₂ = −2.068E−01, A₁₄ = 4.483E−02, A₁₆ =−4.127E−03 Ninth Surface k = 0.000, A₄ = 3.202E−01, A₆ = −3.079E−01, A₈= 1.081E−01, A₁₀ = −1.418E−02, A₁₂ = 2.097E−03, A₁₄ = −1.120E−03, A₁₆ =1.659E−04 Tenth Surface k = 0.000, A₄ = 3.433E−01, A₆ = −2.946E−01, A₈ =1.101E−01, A₁₀ = −1.434E−02, A₁₂ = −4.774E−03, A₁₄ = 1.985E−03, A₁₆ =−1.986E−04 Eleventh Surface k = −7.303E−01, A₄ = −2.668E−01, A₆ =1.616E−01, A₈ = −6.573E−02, A₁₀ = 1.100E−02, A₁₂ = 2.638E−04, A₁₄ =−2.619E−04, A16 = 2.065E−05 Twelfth Surface k = −8.772, A₄ = −9.632E−02,A₆ = 2.910E−02, A₈ = −4.805E−03, A₁₀ = −1.950E−03, A₁₂ = 1.149E−03, A₁₄= −2.097E−04, A₁₆ = 1.332E−05 The values of the respective conditionalexpressions are as follows: f1/f2 = −0.58 f12/f = 0.97 f/f4 = −0.18f34/f = −5.42 D23/L16 = 0.081

Accordingly, the imaging lens of Numerical Data Example 3 satisfies theabove-described conditional expressions. A distance on the optical axisfrom the object-side surface of the first lens L1 to the image plane IM(length in air) is 5.37 mm, and downsizing of the imaging lens isattained.

FIG. 8 shows the lateral aberration that corresponds to the image heightratio H of the imaging lens in Numerical Data Example 3 and FIG. 9 showsthe spherical aberration (mm), the astigmatism (mm), and the distortion(%), respectively. As shown in FIGS. 8 and 9, according to the imaginglens of Numerical Data Example 3, the aberrations are satisfactorilycorrected.

Numerical Data Example 4

Basic data are shown below.

f = 4.45 mm, Fno = 2.1, ω = 33.7° Unit: mm Surface Data Surface Number ir d nd νd (Object) ∞ ∞  1* 1.505 0.722 1.5350 56.1 (=νd1)  2* (Stop)85.933 0.014  3* 6.527 0.279 1.6355 24.0 (=νd2)  4* 2.536 0.626 (=D23) 5* −6.929 0.367 1.6355 24.0 (=νd3)  6* −10.813 0.058  7* −6.966 0.3921.5350 56.1 (=νd4)  8* −14.138 0.047  9* −6.770 0.433 1.5350 56.1 (=νd5)10* −5.674 0.095 11* 1.903 0.768 1.5350 56.1 (=νd6) 12* 1.497 0.200 13 ∞0.300 1.5168 64.2 14 ∞ 0.802 (Image ∞ plane) f1 = 2.84 mm f2 = −6.65 mmf3 = −31.21 mm f4 = −26.07 mm f5 = 57.39 mm f6 = −38.73 mm f12 = 4.13 mmf34 = −14.09 mm L16 = 3.801 mm Aspheric Surface Data First Surface k =0.000, A₄ = −1.949E−04, A₆ = 1.546E−03, A₈ = 1.964E−02, A₁₀ =−7.897E−02, A₁₂ = 9.275E−02, A₁₄ = −4.388E−02 Second Surface k = 0.000,A₄ = −4.512E−02, A₆ = 1.625E−01, A₈ = −2.798E−01, A₁₀ = 1.724E−01, A₁₂ =1.562E−02, A₁₄ = −5.478E−02 Third Surface k = 0.000, A₄ = −9.001E−02, A₆= 2.840E−01, A₈ = −5.679E−01, A₁₀ = 7.287E−01, A₁₂ = −5.035E−01, A₁₄ =1.445E−01 Fourth Surface k = 0.000, A₄ = −3.045E−02, A₆ = 8.348E−02, A₈= −1.307E−01, A₁₀ = 4.219E−01, A₁₂ = −5.812E−01, A₁₄ = 3.320E−01 FifthSurface k = 0.000, A₄ = −4.414E−02, A₆ = −3.260E−01, A₈ = 5.082E−01, A₁₀= −5.958E−01, A₁₂ = 5.999E−01, A₁₄ = −2.767E−01 Sixth Surface k = 0.000,A₄ = −4.248E−02, A₆ = −1.897E−01, A₈ = 2.506E−01, A₁₀ = −7.447E−02Seventh Surface k = 0.000, A₄ = −2.880E−01, A₆ = 5.524E−01, A₈ =−3.988E−01, A₁₀ = 1.408E−01, A₁₂ = −2.117E−02 Eighth Surface k = 0.000,A₄ = −3.910E−01, A₆ = 7.722E−01, A₈ = −8.061E−01, A₁₀ = 5.243E−01, A₁₂ =−2.067E−01, A₁₄ = 4.482E−02, A₁₆ = −4.122E−03 Ninth Surface k = 0.000,A₄ = 3.024E−01, A₆ = −3.066E−01, A₈ = 1.091E−01, A₁₀ = −1.393E−02, A₁₂ =2.138E−03, A₁₄ = −1.118E−03, A₁₆ = 1.655E−04 Tenth Surface k = 0.000, A₄= 3.436E−01, A₆ = −2.943E−01, A₈ = 1.103E−01, A₁₀ = −1.433E−02, A₁₂ =−4.781E−03, A₁₄ = 1.983E−03, A₁₆ = −1.985E−04 Eleventh Surface k =−7.525E−01, A₄ = −2.710E−01, A₆ = 1.639E−01, A₈ = −6.542E−02, A₁₀ =1.101E−02, A₁₂ = 2.568E−04, A₁₄ = −2.641E−04, A₁₆ = 1.990E−05 TwelfthSurface k = −7.073, A₄ = −8.897E−02, A₆ = 2.764E−02, A₈ = −4.789E−03,A₁₀ = −1.922E−03, A₁₂ = 1.152E−03, A₁₄ = −2.098E−04, A₁₆ = 1.317E−05 Thevalues of the respective conditional expressions are as follows: f1/f2 =−0.43 f12/f = 0.93 f/f4 = −0.17 f34/f = −3.17 D23/L16 = 0.16

Accordingly, the imaging lens of Numerical Data Example 4 satisfies theabove-described conditional expressions. A distance on the optical axisX from the object-side surface of the first lens L1 to the image planeIM (length in air) is 5.00 mm, and downsizing of the imaging lens isattained.

FIG. 11 shows the lateral aberration that corresponds to the imageheight ratio H of the imaging lens in Numerical Data Example 4 and FIG.12 shows the spherical aberration (mm), the astigmatism (mm), and thedistortion (%), respectively. As shown in FIGS. 11 and 12, according tothe imaging lens of Numerical Data Example 4, the aberrations are alsosatisfactorily corrected.

Numerical Data Example 5

Basic data are shown below.

f = 4.68 mm, Fno = 2.1, ω = 32.4° Unit: mm Surface Data Surface Number ir d nd νd (Object) ∞ ∞  1* 1.486 0.756 1.5350 56.1 (=νd1)  2* (Stop)−32.618 0.041  3* 8.951 0.294 1.6355 24.0 (=νd2)  4* 2.197 0.575 (=D23) 5* −9.338 0.348 1.6355 24.0 (=νd3)  6* −9.847 0.078  7* −6.818 0.3671.5350 56.1 (=νd4)  8* −16.170 0.076  9* −6.032 0.428 1.5350 56.1 (=νd5)10* −5.370 0.104 11* 1.884 0.736 1.5350 56.1 (=νd6) 12* 1.525 0.200 13 ∞0.300 1.5168 64.2 14 ∞ 0.925 (Image ∞ plane) f1 = 2.67 mm f2 = −4.61 mmf3 = −384.29 mm f4 = −22.26 mm f5 = 74.34 mm f6 = −52.48 mm f12 = 4.55mm f34 = −20.76 mm L16 = 3.803 mm Aspheric Surface Data First Surface k= 0.000, A₄ = −3.926E−04, A₆ = 1.761E−03, A₈ = 1.759E−02, A₁₀ =−7.882E−02, A₁₂ = 9.346E−02, A₁₄ = −4.285E−02 Second Surface k = 0.000,A₄ = −4.072E−02, A₆ = 1.634E−01, A₈ = −2.799E−01, A₁₀ = 1.738E−01, A₁₂ =1.781E−02, A₁₄ = −5.303E−02 Third Surface k = 0.000, A₄ = −8.769E−02, A₆= 2.872E−01, A₈ = −5.686E−01, A₁₀ = 7.325E−01, A₁₂ = −4.958E−01, A₁₄ =1.353E−01 Fourth Surface k = 0.000, A₄ = −2.949E−02, A₆ = 1.028E−01, A₈= −1.293E−01, A₁₀ = 4.297E−01, A₁₂ = −5.767E−01, A₁₄ = 3.418E−01 FifthSurface k = 0.000, A₄ = −5.508E−02, A₆ = −3.087E−01, A₈ = 5.051E−01, A₁₀= −6.231E−01, A₁₂ = 5.923E−01, A₁₄ = −2.434E−01 Sixth Surface k = 0.000,A₄ = −5.170E−02, A₆ = −1.961E−01, A₈ = 2.489E−01, A₁₀ = −7.531E−02Seventh Surface k = 0.000, A₄ = −2.953E−01, A₆ = 5.553E−01, A₈ =−3.984E−01, A₁₀ = 1.407E−01, A₁₂ = −2.136E−02 Eighth Surface k = 0.000,A₄ = −3.880E−01, A₆ = 7.712E−01, A₈ = −8.064E−01, A₁₀ = 5.244E−01, A₁₂ =−2.066E−01, A₁₄ = 4.483E−02, A₁₆ = −4.135E−03 Ninth Surface k = 0.000,A₄ = 3.045E−01, A₆ = −3.067E−01, A₈ = 1.090E−01, A₁₀ = −1.395E−02, A₁₂ =2.151E−03, A₁₄ = −1.120E−03, A₁₆ = 1.690E−04 Tenth Surface k = 0.000, A₄= 3.420E−01, A₆ = −2.942E−01, A₈ = 1.104E−01, A₁₀ = −1.430E−02, A₁₂ =−4.774E−03, A₁₄ = 1.985E−03, A₁₆ = −1.980E−04 Eleventh Surface k =−8.085E−01, A₄ = −2.714E−01, A₆ = 1.639E−01, A₈ = −6.540E−02, A₁₀ =1.102E−02, A₁₂ = 2.602E−04, A₁₄ = −2.643E−04, A₁₆ = 1.987E−05 TwelfthSurface k = −7.858, A₄ = −9.353E−02, A₆ = 2.853E−02, A₈ = −4.858E−03,A₁₀ = −1.930E−03, A₁₂ = 1.151E−03, A₁₄ = −2.095E−04, A₁₆ = 1.323E−05 Thevalues of the respective conditional expressions are as follows: fl/f2 =−0.58 f12/f = 0.97 f/f4 = −0.21 f34/f = −4.44 D23/L16 = 0.15

Accordingly, the imaging lens of Numerical Data Example 5 satisfies theabove-described conditional expressions. A distance on the optical axisX from the object-side surface of the first lens L1 to the image planeIM (length in air) is 5.13 mm, and downsizing of the imaging lens isattained.

FIG. 14 shows the lateral aberration that corresponds to the imageheight ratio H of the imaging lens in Numerical Data Example 5 and FIG.15 shows the spherical aberration (mm), the astigmatism (mm), and thedistortion (%), respectively. As shown in FIGS. 14 and 15, according tothe imaging lens of Numerical Data Example 5, the aberrations aresatisfactorily corrected.

Numerical Data Example 6

Basic data are shown below.

f = 4.11 mm, Fno = 2.2, ω = 35.8° Unit: mm Surface Data Surface Number ir d nd νd (Object) ∞ ∞  1* 1.552 0.686 1.5350 56.1 (=νd1)  2* (Stop)−22.004 0.055  3* 10.096 0.260 1.6355 24.0 (=νd2)  4* 2.181 0.581 (=D23) 5* −17.376 0.283 1.6355 24.0 (=νd3)  6* −16.412 0.062  7* −9.699 0.3481.5350 56.1 (=νd4)  8* −13.337 0.041  9* −8.558 0.380 1.5350 56.1 (=νd5)10* −5.778 0.084 11* 1.785 0.818 1.5350 56.1 (=νd6) 12* 1.591 0.200 13 ∞0.300 1.5168 64.2 14 ∞ 0.910 (Image ∞ plane) f1 = 2.73 mm f2 = −4.39 mmf3 = 413.53 mm f4 = −68.52 mm f5 = 31.63 mm f6 = 57.92 mm f12 = 5.11 mmf34 = −81.37 mm L16 = 3.598 mm Aspheric Surface Data First Surface k =0.000, A₄ = −1.767E−03, A₆ = 3.088E−03, A₈ = 1.608E−02, A₁₀ =−7.735E−02, A₁₂ = 9.643E−02, A₁₄ = −4.410E−02 Second Surface k = 0.000,A₄ = −3.573E−02, A₆ = 1.693E−01, A₈ = −2.785E−01, A₁₀ = 1.771E−01, A₁₂ =1.620E−02, A₁₄ = −6.102E−02 Third Surface k = 0.000, A₄ = −8.316E−02, A₆= 2.926E−01, A₈ = −5.513E−01, A₁₀ = 7.063E−01, A₁₂ = −5.504E−01, A₁₄ =1.834E−01 Fourth Surface k = 0.000, A₄ = −4.204E−02, A₆ = 1.608E−01, A₈= −2.128E−01, A₁₀ = 3.952E−01, A₁₂ = −5.064E−01, A₁₄ = 2.762E−01 FifthSurface k = 0.000, A₄ = −6.828E−02, A₆ = −2.723E−01, A₈ = 4.939E−01, A₁₀= −6.149E−01, A₁₂ = 5.947E−01, A₁₄ = −2.528E−01 Sixth Surface k = 0.000,A₄ = −7.912E−02, A₆ = −2.010E−01, A₈ = 2.598E−01, A₁₀ = −8.081E−02Seventh Surface k = 0.000, A₄ = −2.946E−01, A₆ = 5.469E−01, A₈ =−3.988E−01, A₁₀ = 1.420E−01, A₁₂ = −2.145E−02 Eighth Surface k = 0.000,A₄ = −4.228E−01, A₆ = 7.864E−01, A₈ = −8.057E−01, A₁₀ = 5.235E−01, A₁₂ =−2.070E−01, A₁₄ = 4.483E−02, A₁₆ = −4.098E−03 Ninth Surface k = 0.000,A₄ = 3.027E−01, A₆ = −3.065E−01, A₈ = 1.083E−01, A₁₀ = −1.408E−02, A₁₂ =2.161E−03, A₁₄ = −1.109E−03, A₁₆ = 1.731E−04 Tenth Surface k = 0.000, A₄= 3.516E−01, A₆ = −2.983E−01, A₈ = 1.102E−01, A₁₀ = −1.422E−02, A₁₂ =−4.752E−03, A₁₄ = 1.986E−03, A₁₆ = −1.991E−04 Eleventh Surface k =−7.985E−01, A₄ = −2.713E−01, A₆ = 1.640E−01, A₈ = −6.532E−02, A₁₀ =1.103E−02, A₁₂ = 2.609E−04, A₁₄ = −2.644E−04, A₁₆ = 1.971E−05 TwelfthSurface k = −5.816, A₄ = −8.929E−02, A₆ = 2.946E−02, A₈ = −5.106E−03,A₁₀ = −1.940E−03, A₁₂ = 1.156E−03, A₁₄ = −2.087E−04, A₁₆ = 1.317E−05 Thevalues of the respective conditional expressions are as follows: f1/f2 =−0.62 f12/f = 1.24 f/f4 = −0.060 f34/f = −19.80 D23/L16 = 0.16

Accordingly, the imaging lens of Numerical Data Example 6 satisfies theabove-described conditional expressions. A distance on the optical axisX from the object-side surface of the first lens L1 to the image planeIM (length in air) is 4.91 mm, and downsizing of the imaging lens isattained.

FIG. 17 shows the lateral aberration that corresponds to the imageheight ratio H of the imaging lens in Numerical Data Example 6 and FIG.18 shows the spherical aberration (mm), the astigmatism (mm), and thedistortion (%), respectively. As shown in FIGS. 17 and 18, according tothe imaging lens of Numerical Data Example 6, the aberrations aresatisfactorily corrected.

According to the imaging lens of the embodiment described above, it ispossible to attain an angle of view (2ω) of 70° or greater. Forreference, the angles of view in Numerical Data Examples 1 to 6 arewithin the range of 62.6° to 71.6°. According to the imaging lens of theembodiment, it is possible to take an image in a wider range than aconventional imaging lens.

In addition, in these days, a high resolution imaging element isfrequently combined with an imaging lens for a purpose of improvingcamera performances. Since a light-receiving area of each pixel issmaller in case of such high resolution imaging element, an image takentends to be dark. As a method to correct such darkness, there is amethod of improving light-receiving sensitivity of an imaging elementusing an electric circuit. However, when the light-receiving sensitivityis high, a noise component that does not directly contribute to imageformation is also amplified, so that another circuit is required toreduce the noise. According to the Numerical Data Examples 1 to 6, Fnois very small, i.e. as small as 2.0 to 2.3. According to the imaginglens of the embodiment, it is possible to obtain a sufficiently brightimage without the above-described electric circuit.

Accordingly, when the imaging lens of the embodiment is applied in anoptical system such as a camera to be mounted in a portable deviceincluding cellular phones, portable information terminal, andsmartphones, digital still cameras, security cameras, vehicle onboardcameras, and network cameras, it is possible to attain both highfunctionality and downsizing of the cameras.

The invention can be applied in an imaging lens for mounting in arelative small camera, such as cameras mounted in portable devicesincluding cellular phones, smartphones, and portable informationterminals, digital still cameras, security cameras, vehicle onboardcameras, and network cameras.

The disclosure of Japanese Patent Application No. 2012-116110, filed onMay 22, 2012, is incorporated in the application by reference.

While the invention has been explained with reference to the specificembodiments of the invention, the explanation is illustrative and theinvention is limited only by the appended claims.

What is claimed is:
 1. An imaging lens comprising: a first lens havingpositive refractive power; a second lens having negative refractivepower; a third lens; a fourth lens having negative refractive power; afifth lens having positive refractive power; and a sixth lens, arrangedin this order from an object side to an image plane side, wherein saidfirst lens is formed in a shape so that a surface thereof on the objectside has a positive curvature radius, said second lens is formed in ashape so that a surface thereof on the image plane side has a positivecurvature radius, said fifth lens is formed in a shape so that a surfacethereof on the object side and a surface thereof on the image plane sidehave negative curvature radii, and each of said third lens, said fourthlens, said fifth lens, and said sixth lens has refractive power weakerthan that of each of the first lens and the second lens.
 2. The imaginglens according to claim 1, wherein said fourth lens is formed in a shapeso that a surface thereof on the object side and a surface thereof onthe image plane side have negative curvature radii.
 3. The imaging lensaccording to claim 1, wherein said sixth lens is formed in a shape sothat a surface thereof on the object side and a surface thereof on theimage plane side have positive curvature radii.
 4. The imaging lensaccording to claim 1, wherein said first lens has a focal length f1, andsaid second lens has a focal length f2 so that the following conditionalexpression is satisfied:−0.7<f1/f2<−0.3.
 5. The imaging lens according to claim 1, wherein saidfirst lens and said second lens have a composite focal length f12 sothat the following conditional expression is satisfied:0.8<f12/f<1.5 where f is a focal length of a whole lens system.
 6. Theimaging lens according to claim 1, wherein said fourth lens have a focallength f4 so that the following conditional expression is satisfied:−0.3<f/f4<−0.01 where f is a focal length of a whole lens system.
 7. Theimaging lens according to claim 1, wherein said third lens and saidfourth lens have a composite focal length f34 so that the followingconditional expression is satisfied:−20.0<f34/f<−1.0 where f is a focal length of a whole lens system. 8.The imaging lens according to claim 1, wherein said second lens has asurface on the image plane side situated away from a surface of thethird lens on the object side by a distance D23 on an optical axis, andsaid first lens has the surface on the object side situated away from asurface of the sixth lens on the image plane side by a distance L16 onthe optical axis so that the following conditional expression issatisfied:0.05<D23/L16<0.3.
 9. The imaging lens according to claim 1, wherein eachof said first lens has an Abbe's number νd1, said fourth lens has anAbbe's number νd4, said fifth lens has an Abbe's number νd5, and saidsixth lens has an Abbe's number νd6 so that the following conditionalexpressions are satisfied:45<νd1<7545<νd4<7545<νd5<7545<νd6<75.
 10. The imaging lens according to claim 1, wherein each ofsaid second lens has an Abbe's number νd2 and said third lens has anAbbe's number νd3 so that the following conditional expressions aresatisfied:20<νd2<4020<νd3<40.